Sandra Redman consoles her neighbor, Vicki Simpson, center, after she rode out a tornado from the safety of her rural Wadesville, Ind., basement Friday. Her husband, Byron, phoned her from Wadesville and told her to get in the basement "now." Both of Simpson's dogs, Bella and Echo, stayed in the garage since Simpson didn't have time to let them inside the home. The garage was demolished, but the dogs were fine.

On Friday, what the National Weather Service called an “enormous outbreak” of up to 91 deadly twisters killed at least 31 people and put millions at risk as it rolled through the Ohio and Tennessee Valleys, destroying nearly the entire towns of Marysville, Ind. and Henryville, Ind., which both have a population of about 2,000, as the system spanned an area from the Gulf to the Great Lakes.

The weather service had issued 269 tornado warnings across the region by 10 p.m. Friday, compared to 189 warnings that were issued in the entire month of February.

As dawn broke on Saturday, rescue crews continued to search wide swaths of debris in several states, using rescue dogs and heat-detectors to look for survivors trapped in debris.

Many Kentucky towns remained cut off and searchers in Indiana spanned out across wide rural areas to assess damage and find possible survivors. Of the 31 victims, 15 were in Indiana, 12 in Kentucky, three in Ohio and one in Alabama, but officials said the toll could be worse.

“We are going to continue to hit every county road that we know of that there are homes on and search those homes,” Indiana State Police Sgt. Jerry Goodin told the Associated Press. “We have whole communities and whole neighborhoods that are completely gone. We’ve had a terrible, terrible tragedy here.”

The storm was unusual in and of itself, but what was called a one-in-20-year event was made more so by the fact that it came less than a year after a historic tornado outbreak on April 27, 2011, that left hundreds dead and billions in damage, mostly in Alabama.

Earlier this week, Greg Carbin, a forecaster with NOAA's Storm Forecasting Center in Norman, Okla., said the climatological odds were long that the country would see two extremely active tornado seasons in a row, although forecasters have predicted higher-than-usual numbers of twisters this year.

This week, however, America saw two massive tornado-spewing systems move through the same part of the country in the span of three days. On Wednesday, a system that spawned more than 20 tornadoes killed 13 people in Kansas, Missouri, Illinois, and Tennessee, leveling parts of Harrisburg, Branson, Mo., and Harveyville, Kan.

On Friday, Doppler radar maps again were showing huge swaths of red, indicating intense atmospheric turbulence as spring-time warmth clashed with late-winter cold fronts, as sirens blared and Americans raced for cellars and other shelter.

Madison County, Ala., which took a direct hit last April, watched as another tornado took a similar trek through the county on Friday, injuring at least seven people.

As that system continued into eastern Tennessee, at least two tornadoes were spotted, one near Lookout Mountain on the Georgia border, injuring 29 people. The storm forced the Tennessee Valley Authority to power down the Sequoyah nuclear power plant to 70 percent power.

A tornado also left at least a possible eight-mile path of destruction in northeast Tennessee, stretching into Virginia, but damage assessments were not expected until after daybreak on Saturday.

Multiple tornadoes descended on Indiana, where the small town of Marysville was flattened, the tornado sparing only the town's water tower. In Henryville, students who were about to be sent home were forced to huddle in hallways as a tornado damaged parts of the building. No one was injured.

"All of this happened in less than 30 seconds," Cory Thomas, a Hanover volunteer firefighter, told pal-item.com, a local news site.

In Kentucky, a tornado flattened the local fire house in Milton and flattened most of the small town of West Liberty, killing three and injuring 75. All the town's schools were destroyed, and local officials reporting that few recognizable structures remained in West Liberty.